In order to achieve planing speedboats, it is often necessary to install several drives in one hull. One type of boat which is driven at planing speeds consists of boats with a V-shaped hull designed for planing. With such a hull, a drive is suspended on each side of the center line of the hull. The drives comprise an underwater housing projecting downwards from the outside of the hull, which housing can be rotated in relation to the hull. An at least essentially vertical drive shaft is mounted in the underwater housing in such a way that it can rotate. The drive shaft drives an at least essentially horizontal propeller shaft via a bevel gear comprised in the underwater housing. Such a type of boat is known through, for example, SE-9402272-0.
For maneuvering such boats, the angle of rotation of the underwater housing around the axis of rotation of the underwater housing is set via a servo motor. The servo motor is controlled by a control unit which, in addition to an input signal corresponding to the required position of the underwater housing, receives an input signal from a position sensor arranged to detect the set angular position of the underwater housing.
In order to be able to obtain good operating economy and performance and to reduce wear on bearings incorporated in the drives, it is important that the propeller shafts can be aligned in a parallel position. It is therefore important to calibrate the position sensors in a reference position when the propeller shafts are aligned parallel to each other and to the keel line of the boat.
Conventionally, the position sensors are calibrated by the output signal from the position sensors being stored in a control unit after the propeller shafts have been placed in a parallel position. The parallel alignment is verified by the use of a mechanical tool which is fitted onto the respective propeller shaft or underwater housing. The mechanical tool comprises two mechanically-connected adapters which are fitted onto their respective underwater housing into a docking module arranged for the purpose. The fitting can only be carried out when the propeller shafts are parallel, as the mechanical tool consists of a rigid measure. Such a method for parallel alignment and such a tool for parallel alignment have considerable disadvantages. Firstly, a tool must be produced for each type of boat, as the tool cannot be used for boats of different dimensions. In addition, the underwater housing and tool can be subjected to large forces if the tool is fitted onto the underwater housings or the propeller shafts when they are in a position that is not completely parallel. In addition, after such an incorrect fitting, the tool can be deformed, so that it can no longer be used for parallel alignment of the propeller shafts.